Method and apparatus for driving a continuous current in a toroidal plasma

Abstract

Method and apparatus for continuously driving a current in a toroidal plasma through r-f induced, asymmetric trapping or detrapping. The method and apparatus may be used to supply ohmic current over a prolonged or indefinite time period and thus provide for steady state operation of toroidal plasma apparatus such as tokamaks.

What is claimed is: 
     
       1. In apparatus for generating and confining a toroidal plasma comprising means for providing a toroidal magnetic field in a plasma zone, said toroidal field being of increasing strength with decreasing radial distance from the major toroidal axis, and means for generating a plasma in the plasma zone, said plasma having a dynamic trapped particle population of electrons, which reflect back and forth along the minor toroidal axis without contributing to the net toroidal plasma current, the improvement comprising means for asymmetrically altering the trapped electron particle population with respect to the minor toroidal axis to produce an ohmic plasma current along the minor toroidal axis. 
     
     
       2. Apparatus in accordance with claim 1 wherein said trapped particle population altering means comprises means for asymmetrically trapping plasma electrons. 
     
     
       3. Apparatus in accordance with claim 2 wherein said trapping means comprises means for providing an r-f field which propagates in a direction parallel to the plasma-confining magnetic field, said r-f field having an electric field vector perpendicular to said confining field, and being at resonance with a plasma resonance frequency, to increase electron perpendicular velocity. 
     
     
       4. Apparatus in accordance with claim 3 wherein said frequency is an electron cyclotron resonance frequency. 
     
     
       5. A method for providing a toroidal plasma current comprising the steps of providing a toroidal magnetic field in a plasma confinement zone, said toroidal field being of increasing magnetic strength with decreasing distance from the major toroidal axis,   providing a plasma in said plasma zone and an initial toroidal current in said plasma to produce a poloidal field, said toroidal field and said poloidal field producing a plasma confining magnetic field, said plasma having a dynamic trapped particle population of electrons which reflect back and forth along the minor toroidal axis without contributing to the net toroidal plasma current, and   increasing the electron perpendicular velocity to asymmetrically trap plasma electrons with respect to the minor toroidal axis to produce a net current in said plasma.   
     
     
       6. A method in accordance with claim 5 wherein said electron perpendicular velocity is increased by applying an r-f field which propagates in a direction parallel to the plasma confining magnetic field, said r-f field having an electric field vector perpendicular to said confining field and being at resonance with a plasma resonance frequency to increase electron perpendicular velocity. 
     
     
       7. A method in accordance with claim 6 wherein said frequency is an electron cyclotron resonance frequency. 
     
     
       8. Apparatus in accordance with claim 1 further including means for applying counter-current r-f ion cyclotron resonance energy to cancel ion momentum resulting from electron friction. 
     
     
       9. A method in accordance with claim 5 further including the step of applying counter current r-f ion cyclotron resonance energy for cancelling ion momentum from electron friction.